1. Field of the Invention
The present invention relates to a zoom lens system, and particularly relates to a zoom lens system that includes plastic aspheric lenses and a resin hybrid lens to reduce the overall length and the cost. The zoom lens system further includes two pairs of cemented lenses and a pair of abutting lenses to facilitate assembly.
2. Description of Prior Art
Conventionally, an optical lens system is composed of a plurality of spherical lenses. However, spherical lenses cannot focus light from the center and periphery to the same point, which is called “spherical aberration”. The solution is to employ a number of additional spherical correction lenses or to introduce an aspheric surface. However, the employment of additional spherical correction lenses results in increase of the cost and elongation of the length of the lens system. The introduction of an aspheric surface effectively corrects aberration, and a corresponding aspheric lens functions equivalent to several spherical lenses, whereby the cost can be reduced and a compact lens system can be ensured. In addition, an aspheric lens is generally made of plastic such as compound resin by injection molding. This facilitates a large-scale and efficient manufacture, and thus further decreases the cost.
When designing a zoom lens system, various factors must be considered to effectively correct various aberrations at different focal lengths due to zooming of the zoom lens system. Various conventional zoom lens system designs are disclosed in U.S. Pat. Nos. 6,744,571, 6,014,268, 5,712,733, and 5,103,343. FIGS. 1A and 1B illustrate two examples of the conventional zoom lens systems. However, in these conventional designs, to provide a four-times zoom ratio, three lens groups are generally adopted, which necessitates a long overall length of the zoom lens system. When four lens groups are adopted, the number of the constituent lenses and the manufacture cost are generally increased.